1. Chapter 9
Work and Energy

2. Work and Power
Work- a quantity that measures the effects of a force acting over a distance.
W=f x d
Measured (SI) in joules
Power- a quantity that measures the rate at which work is done.
P=W/t
Measured (SI) in watts (W)

3. Simple Machine- a simple device for altering the magnitude or direction of a force.
lever, inclined plane
Compound machine-
machine made of more than one simple machine.
scissors, car jacks, & bicycle.
Complex machine-
machine made of more than one compound machine.
car, tractor, etc…

4. 9.2 Simple Machines The Lever Family
simple lever- hammer, crowbar, broom, etc…
divided into three classes: 1st, 2nd, & 3rd.
All levers have a rigid arm that turns
around a point called the fulcrum.
pulley- modified lever.
fixed, moveable, block & tackle
wheel & axle- pulley connected to a shaft.
screwdriver & steering wheels

5. The inclined plane family
Ramps- multiply and redirect the force.
roads, loading docks, etc…
Wedge- modified incline plane, two inclined planes back to back.
axe, knife, & nails.
Screw- inclined plane wrapped around
a cylinder.
bolts, jar lids, & spiral stairs.

6. Machines- multiply and redirect forces to make work easier.
Mechanical advantage- a quantity that measures how much a machine multiplies force or distance.
MA= of/if or MA= id/od

7. 9.3 What is Energy? Energy- the ability to do work. measured in Joules
Potential energy- the stored energy resulting from the relative positions of objects in a system.
Chemical energy
Elastic potential energy
Gravitational potential energy
PE= mgh

8. Kinetic energy- the energy of a moving object due to its motion.
depends on mass but more on speed.
KE=½mv²
Mechanical energy- the sum of the kinetic and potential energy of large-scale objects in a system.
Non mechanical energy- energy at the level of atoms that does not affect motion on a large scale.

9. Solar energy- energy from the sun.
Electrical energy- charged particles (electrons) flowing through wires or other conducting materials.
Light energy- electromagnetic waves.

10. Potential and Kinetic Energy

11. 9.4 Conservation of Energy
Energy transformations- changing from one form of energy to another form.
KE PE thrown ball at it’s apex
PE KE apple falling from tree
Chemical  KE fire cracker
Law of Conservation of Energy- energy cannot be created or destroyed

12. Energy Transformations

13. Efficiency of Machines
* not all work done by a machine is useful work. Lose some due to friction
and other factors.
Efficiency- a quantity that measures the ratio of useful work output to work input, usually expressed as a percentage.
efficiency = useful work output
work input

14. efficiency

15. Law of conservation of energy